Layer Brownies: In a large trifle dish or glass bowl, place a layer of brownie squares at the bottom.
Add Peanut Butter Mousse: Spread a layer of peanut butter mousse over the brownies.
Add Whipped Topping: Add a layer of whipped topping over the mousse.
Repeat Layers: Continue layering brownies, peanut butter mousse, and whipped topping until the dish is filled, ending with a layer of whipped topping.
Garnish: Sprinkle the top with chopped peanuts or chopped peanut butter cups for garnish.